1. Field of the Invention
The present invention generally relates to the treatment of industrial and municipal waste waters. The invention more particularly concerns a multiple-stage supercritical and catalyzed wet oxidation system aimed at providing a more rapid and complete degradation of organic and inorganic compounds in industrial and municipal waste waters.
2. Description of the Prior Art
wet oxidation of waste water and sludge has been used since the 1960s. These waste streams may vary widely in composition. For example, municipal waste water typically contains relatively large amounts of organic matter and small amounts of minerals. Industrial waste streams or sludges may contain organic matter which is unlike the organic matter contained in municipal waste, in addition to relatively larger amounts of mineral matter.
One commercial application of wet oxidation is a wet oxidation process conducted at subcritical conditions for water. This process, however, only partially degrades the waste materials and produces relatively large amounts of low molecular weight organic compounds. To achieve more complete and effective destruction of hazardous waste materials, recent investigations of wet oxidation have been directed at above the critical point of water, or at the use of catalysts.
Supercritical water oxidation has been demonstrated in some lab-scale tests to be more effective than subcritical wet oxidation. Catalysis studies have also shown that many metals, metal oxides, or metal ions actively take part in subcritical wet oxidation processes. One subcritical wet oxidation process has employed water soluble copper and silver ions as catalysts, in concentrations between 10 ppm and 10,000 ppm.
Another known process suggests a flow sequence which includes (1) pressurization of a feedstock, (2) injection of compressed oxygen gas into the feedstock, (3) heating the feedstock by heat exchange with the hot reactor effluent, (4) control of reaction temperature using a heater, and (5) catalytic oxidation of organic compounds in a single reactor.
Hydrogen peroxide has been used as a catalyst for wet oxidation of phenol in subcritical water. Hydrogen peroxide (ag.) or ozone (ag.) have also been used as a sole source of oxidant in supercritical water oxidation.
Transition element catalysts have been used in catalytic processes for degradation of organic materials in aqueous and organic fluids in efforts to produce environmentally compatible products.
Several methods have also been used or proposed for removing residue solids from a reactor in wet oxidation processes. One known practice involves shutting down the wet oxidation system, completely draining the reactor, and then physically removing the solids. Other methods suggest periodic removal of solids from a wet oxidation reactor, with only a temporary suspension of feed to the plant, without draining the entire liquid portion of the reactor contents, and without cooling the reactor contents.
Still another method suggests a two zone pressure vessel in which precipitates and other solids fall or are sprayed from a supercritical temperature upper zone into a lower temperature lower zone. The feed material may include various waste products which are substantially oxidized in the upper zone of the pressure vessel. A brine or slurry which forms at the lower temperature sub zone of the vessel is removed via a pipe and disposed of.
While the systems of the prior art have proved able to attack the waste materials in waste waters and sludges, further improvements are needed for better efficiency and effectiveness. As noted, for example, the existing systems tend to produce products which can be toxic and undesirable in themselves. The catalytic systems are subject to poisoning, and the catalysts, therefore, tend to require frequent regeneration or replacement with attendant high down time and operating costs.